Look at these examples:

Christina's house
my father's books

- We often use the possessive  's with a personal noun  (eg. Christina's house) to   show possession.

This is Christina's house ( = a house that belongs to Christina)

- We also use the possessive 's with other meanings. For example:

Christina's sister is a biologist ( =the sister that Christina has)
Where is your teacher's house? (=the house where your teacher lives)

- We can use the possessive without a following noun (instead of repeating the noun)

Those aren't my students. They are Rodolfo's. (= Rodolfo's students)


- Write  's with a singular noun.   My father's books

- Write only ' with a plural noun ending in  's.  My parents' house

- Write 's with a plural noun not ending in -s.  The children's teacher


my sister's car ( one sister)
my sisters' car ( more than one sister)

- Compare the possessive 's and of ...

We normally use the possessive 's for people and for animals

The cat's milk ( Not: the milk of the cat)
Christina's husband (Not: The husband of Christina)

We normally use  of... for things

the end of the school term
The leg of the table